The operating speed and computing power of computers and computerized devices has increased dramatically over the past several years. The computers of today are able to operate many times faster than those produced just a few years ago, and this treNd shows no sign of stopping. An important part of these speed increases have been increases in the speed and size of computer memories. Computer memories serve as a short term storage location where a computer's processor can store programs, data, and other information that needs to be accessed relatively quickly. Most computer memories are composed of multiple dynamic random access memory (“DRAM”) devices arranged on memory modules, such as dual inline memory modules (“DIMMs”). The memory modules are typically coupled in parallel along a memory channel within the computer. This type of memory arrangement is known as a “multi-drop bus.”
As processors have become faster and computer programs have become more complex, the amount of memory in a typical computer and the speed of that memory have increased. Unfortunately, memory operating at these increased speeds becomes more susceptible to signal integrity problems, which also become more prevalent as more and more memory is placed on the multi-drop bus. This leads to one important limitation of conventional multi-drop bus memory systems, the faster the memory devices operate, the less of them that can he used in a computer and vice-versa. The practical effect of this is that computer system designers are sometimes forced to make a tradeoff between memory speed and memory capacity. Customers, however, are demanding both at the same time while also demanding the ability to employ this greater amount of faster memory on existing multi-drop bus systems.